The cloud over the company at the centre of Wednesday's explosions in Tianjin thickened on Sunday, with mainland media reporting that warnings from other logistics companies in the area about potentially dangerous chemical leaks fell on deaf official ears.

Adding to the mystery were reports citing one Ruihai International Logistics shareholder as saying he was only holding the shares for someone else.

One unidentified industry insider told financial magazine Caijing that people had smelled chemicals near Ruihai's warehouse for as long as the company had been in the Tianjin Port area. Other firms reported fears of a chemical leak to the authorities but there was no response.

An executive at Zhonglian Jiantong International Logistics, which has premises next to Ruihai, said Zhonglian was informed verbally that Ruihai was licensed to handle low-level hazardous chemicals but he did not know how dangerous the goods were.

Ruihai, founded in 2012 with 10 million yuan (HK$12 million) in registered capital, leased a yard from another logistics company for 5.1 million yuan a year and turned the site into warehouses to handle hazardous chemicals last year, Caijing reported.

Ruihai is one of the smaller of the 40 logistic companies in the area but is the only one with a permit to handle hazardous chemicals. That permit requires the approval of firefighting, work safety and maritime authorities.

Caijing claimed Ruihai's shareholders had government connections who had helped to secure the permit for the company. The firm had two shareholders - Li Liang, who held 55 per cent stake of the firm, and Shu Zheng, who had the remainder.

But Shu, a public servant in Tianjin, told Tencent's financial news portal Prism that he had simply lent his identity card to a friend and had been unaware that he was a shareholder of Ruihai.

Shu said he did not know Li nor Ruihai general manager Zhi Feng, who was injured in the blast. He also denied any involvement in the company's daily operations or signing any document as a shareholder.

Shu said his friend was a senior executive at Ruihai but refused to reveal the friend's identity.